In computers and other electronic devices, a configuration illustrated in FIG. 1 is employed to cool a semiconductor device such as a large scale integration (LSI) device. In FIG. 1, rear faces of LSI devices 102a and 102b, which are opposite to connection faces with solder bumps 103 for bonding the LSI devices 102a and 102b to a circuit board 101, are heat dissipating surfaces. The heat dissipating surfaces of the LSI devices 102a and 102b are thermally in contact with a heat spreader or a heat sink 130 to prevent temperature rise of the LSI devices 102a and 102b. 
It is predicted that the amount of heat generated from the LSI devices 102a and 102b will increase along with further progress of integration and device performances. It is also expected that the size and the shape of the heat spreader or the heat sink 130 will become larger and more complicated.
It has been proposed to use a metal core substrate in place of an inexpensive resin substrate to efficiently remove heat from the connection side of the LSI device. See, for example, Patent Documents 1-3 listed below. Another known approach is to refine the structure of the heat sink. It has also been proposed to incorporate a heat pipe structure or a micro-groove structure in the heat sink to improve the cooling efficiency using a coolant. See, for example, Patent Documents 4-6 listed below.
However, it is worrying that the technique for using a metal core substrate to remove heat as disclosed in Patent Documents 1 and 2 will cause complication and cost increases of the manufacturing process of printed circuit boards. There is also fear that the possibility of equipment design is limited. An interposer using a metal core substrate as disclosed in Patent Document 3 is disadvantageous from the viewpoint of connection reliability and cost because a heat-rejecting interposer is inserted between a board and an LSI chip.
Patent Documents 4 and 5 disclose a structure in which a heat pipe is implemented inside the base of a heat sink provided on the rear face of an LSI chip, opposite to the solder connection side. With this structure, the cooling efficiency is expected to be improved compared with the conventional techniques. However, the temperature distribution in the package board increases when the heat generation of each of the LSI chips increases in a System-in-Package or a 3D-stacked LSI package with heterogeneous integration of multi-chip modules. Accordingly, thermal diffusion or heat dissipation of a heat sink placed on the rear face of the LSI chip is unlikely to be sufficient. In addition, the conventional structure with a heat sink provided on the rear face of the LSI chip requires a thermal interface material between the LSI and the heat sink (having a built-in heat pipe) to guarantee thermal contact to the LSI chip. Since thermal resistance is produced in the thermal interface material, significant improvement in cooling efficiency may not be expected.
Patent Document 6 discloses a technology for forming a micro channel inside the heat sink provided on the rear face of the LSI chip to circulate a coolant to cool the LSI chip. The manufacturing and assembling of this cooling system are complicated and there is a problem in reliability due to leakage of coolant.
There is a demand for a cooling mechanism and structure and a manufacturing method of a semiconductor package that can efficiently remove heat from a heat source such as a semiconductor device without making a significant change to the specifications of a conventional heat rejecting system such as a heat spreader or a heat sink.